Target Quality

Table of Contents

1. Description
2. Requirements
3. Commands
4. Example of usage

Description

Target Quality has a really simple goal, instead of guessing what the CQ/CRF value to choose for desired level of video quality we set quality level we want and let the algorithm find CRF/CQ value that will result in that score, for each segment. Which simultaneously achieve 3 things, if compared to usual, single value CRF/CQ encode.

• Ensuring better level of visual consistency than default rate controls
• Give enough bitrate to complex segments to match target quality.
• Save bitrate by not overspending on scenes, which saves bit rate.

Metrics

Target Quality supports the following metrics:

• VMAF
• SSIMULACRA2
• Butteraugli
• XPSNR

Requirements

Depends on the specified Target Metric (--target-metric)

VMAF

• Working VMAF setup
  • FFMPEG with libvmaf (It's de facto default configuration from 2020)
  • Installed or manually selected VMAF models
    • by default it grabs /usr/share/model/vmaf_v0.6.1.pkl

SSIMULACRA2

• VapourSynth
  • VapourSynth plugin Vapoursynth-HIP for Hardware-accelerated processing (recommended) or Vapoursynth-Zig Image Process for CPU processing
  • Chunk Method must be either lsmash, ffms2, bestsource, or dgdecnv

Butteraugli

• VapourSynth
  • VapourSynth plugin Vapoursynth-HIP for Hardware-accelerated processing (recommended) or vapoursynth-julek-plugin for CPU processing
  • Chunk Method must be either lsmash, ffms2, bestsource, or dgdecnv

XPSNR

• Working FFMPEG XPSNR setup
  • FFMPEG with libxpsnr
  • Probing Rate must be 1 or unspecified

Alternatively:

• Working VapourSynth XPSNR setup
  • VapourSynth plugin Vapoursynth-Zig Image Process
  • Chunk Method must be either lsmash, ffms2, bestsource, or dgdecnv

Encoders

• Quality/Constant Rate control (Target quality change crf/cq value for each segment). Which means that encoders must be in mode that use CRF/CQ and have those options specified ( --crf 30, --cq-level=30) those values get replaced for each segment

Commands

• --target-metric TargetMetric - Chooses the metric used to evaluate quality of each segment

• --target-quality FLOAT-FLOAT - enables target quality with default settings for that encoder, targets a range with FLOAT values

• --probes INT - Overrides maximum amount of probes to make for each segment (Default 4)

• --probe-res "INTxINT" - Overrides the resolution of the probes during calculation

• --probing-rate INT - Divides the framerate of the probes by this value (Default 1)

• --probing-speed ProbeSpeed - Overrides the default or specified preset/cpu-used/speed for that encoder

• --probe-slow - Overrides the default settings for that encoder with the specified settings from --video-params

More details can be found in the Target Quality CLI documentation

Example of usage

av1an -i file --target-quality 90 - Will run aomenc with default settings of target-quality

av1an -i file --target-quality 95 --vmaf_path "vmaf_v.0.6.3.pkl" --probes 6 - With specified path to vmaf model and 6 probes per segment

av1an -i file --encoder rav1e --target-metric ssimulacra2 --target-quality 90 --probing-rate 2 - Will run rav1e with default settings and probe every other frame with SSIMULACRA2

av1an -i file --encoder svt-av1 --video-params "--preset 2 --enable-variance-boost 1" --target-metric butteraugli-3 --target-quality 2 --probe-slow --probing-rate 3 - Will run svt-av1 with preset 2 and variance-boost enabled and probe 1 of every 3 frames with Butteraugli 3-Norm

av1an -i file --encoder x264 --video-params "--preset placebo --tune film" --target-metric xpsnr --target-quality 45 --probe-slow --probing-speed medium - Will run x264 with preset slower and tune film with XPSNR

Scaling

By default VMAF calculation is done at 1920x1080 with default model. VMAF calculation resolution can be changed

--vmaf-res 3840x2160

Calculations with other metrics can be changed as well

--probe-res 1280x720

Cropping with target quality

Filter with crop should be supplied for both ffmpeg options and vmaf filter

--ffmpeg "-vf crop=3840:1900:0:0" --vmaf-filter "crop=3840:1900:0:0" --vmaf-res "3840x1900"

or cropping and resizing could be done with vapoursynth script -i 4k_crop.vpy --vmaf-res "3840x1600" --target-quality 90 -o test.mkv -i 4k_crop.vpy --probe-res "1920x800" --target-quality 3 --target-metric butteraugli-3 -o test.mkv